LT3508 Datasheet, PDF (1/24 Pages) Linear Technology – Dual Monolithic 1.4A Step-Down Switching Regulator

FEATURES
n _{Wide Input Voltage Range: 3.7V to 36V}
n _{Two 1.4A Output Switching Regulators with Internal}
Power Switches
n _{Adjustable 250kHz to 2.5MHz Switching Frequency}
n _{Synchronizable over the Full Frequency Range}
n _{Anti-Phase Switching Reduces Ripple}
n _{Uses Small Inductors and Ceramic Capacitors}
n _{Accurate Programmable Undervoltage Lockout}
n _{Independent Tracking, Soft-Start and Power Good}
Circuits Ease Supply Sequencing
n _{Output Adjustable Down to 800mV}
n _{Small 4mm × 4mm 24-Pin QFN or 16-Pin Thermally}
Enhanced TSSOP Surface Mount Packages
APPLICATIONS
n _Automotive
n _{DSP Power Supplies}
n _{Wall Transformer Regulation}
n _{DSL and Cable Modems}
n _{PCI Express}
LT3508
Dual Monolithic 1.4A
Step-Down Switching
Regulator
DESCRIPTION
The LT^®3508 is a dual current mode PWM step-down
DC/DC converter with internal power switches capable of
generating two 1.4A outputs. The wide input voltage range
of 3.7V to 36V makes the LT3508 suitable for regulating
power from a wide variety of sources, including automo-
tive batteries, 24V industrial supplies and unregulated wall
adapters. Both converters are synchronized to a single os-
cillator programmable up to 2.5MHz and run with opposite
phases, reducing input ripple current. Its high operating
frequency allows the use of small, low cost inductors and
ceramic capacitors, resulting in low, predictable output
ripple. Each regulator has independent tracking and soft-
start circuits and generates a power good signal when its
output is in regulation, easing power supply sequencing
and interfacing with microcontrollers and DSPs.
Cycle-by-cycle current limit, frequency foldback and ther-
mal shutdown provide protection against shorted outputs,
and soft-start eliminates input current surge during start-
up. The low current (<2μA) shutdown mode enables easy
power management in battery-powered systems.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
3.3V and 5V Dual Output Step-Down Converter with Output Sequencing
V_IN
5.6V TO 36V
OUT1
3.3V
1.4A
6.8μH
35.7k
11.5k
22μF
4.7μF
V_IN
BOOST1
0.22μF
SW1
SHDN
BOOST2
SW2
LT3508
51k
150pF
FB1
FB2
V_C1
V_C2
TRACK/SS1 PG1
TRACK/SS2 PG2
GND R_T/SYNC
ON OFF
0.22μF _10μH
OUT2
5V
1.4A
56.2k
43k
10.7k
10μF
100k
1nF
52.3k 100pF
f_SW = 700kHz
POWER
3508 TA01a GOOD
95
V_IN = 12V
90
85
Efficiency
V_OUT2 = 5V
V_OUT1 = 3.3V
80
75
70
65
0
0.5
1
LOAD CURRENT (A)
1.5
3508 TA01b
3508fb
1